1. Field of the Invention
The present invention relates to a method and apparatus for representing an image, and, in addition, a method and apparatus for comparing or matching images, for example, for the purposes of searching or validation.
2. Description of the Background Art
The present invention relates to improvements upon the image identification techniques disclosed in co-pending European patent application No: EP 06255239.3 and UK patent application No: GB 0700468.2 (references [6] and [7] infra). The contents of EP 06255239.3 and GB 0700468.2 are incorporated herein by reference. Details of the inventions and embodiments in EP 06255239.3 and GB 0700468.2 apply analogously to the present invention and embodiments.
The image identification methods and apparatuses described in EP 06255239.3 and GB 0700468.2, which, in each case, extracts a short binary descriptor from an image (see FIG. 2) address many of the drawbacks of the prior art and in particular are characterised by:                reduced computational complexity for both feature extraction and matching,        reduced image descriptor size,        increased robustness to various image modifications, and        reduced false alarm rate to 1 ppm level while maintaining detection rate of over 98% for a wide range of image modifications.        
However, in many practical applications it is necessary for the false alarm rate to be significantly lower than 1 ppm and desirable for the detection rates to be above 98%. Accordingly, it would be desirable to increase the average detection rate to above 98%. In addition, it would be desirable to improve robustness to histogram equalisation and image cropping.